Non-oriented electromagnetic steel sheet, method for producing same, and rotary electric machine containing same

Abstract

(Problem) To provide a novel non-oriented electromagnetic steel sheet that has excellent magnetic aging resistance and does not tend to develop stretcher strain, a method for producing the same, and a rotary electric machine containing the same. (Solution) A non-oriented electromagnetic steel sheet comprising a chemical composition of, in mass%, C: 0.0100% or less, Si: 2.6-4.5% inclusive, Mn: 0.10-3.00% inclusive, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10-2.00% inclusive, one or more selected from Sn and Sb: 0-0.200%, Cr: 0.001-5.000%, predetermined amounts of optionally added elements (Ni, Cu, Ca, Mg, REM, Ti, B, O), and remainder: Fe and impurities, the non-oriented electromagnetic steel sheet being characterized in that the difference: A.I. in the lower yield point before and after aging when aged for one hour at 100°C after application of 8% strain is less than 40 MPa; a method for producing the same; and a rotary electric machine containing the same.

Description

Non-oriented electrical steel sheet, its manufacturing method, and rotating electrical machine including the same

[0001] The present invention relates to a non-oriented electrical steel sheet, a method for manufacturing the same, and a rotating electrical machine including the same.

[0002] Recently, global environmental issues have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there has been a strong demand in recent years for higher efficiency in electrical equipment. For this reason, there has been an increasing demand for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as iron core materials for motors and the like. This trend is particularly evident in motors for electric vehicles and hybrid vehicles, and compressor motors, where the efficiency of motors has been increasing in recent years.

[0003] Automobile drive motors and the like may experience temperature increases during use, and if magnetic aging occurs in that temperature range, the magnetic properties will naturally deteriorate over time compared to when the material was delivered.

[0004] Furthermore, in automobile drive motors and the like, stretcher strain can occur when the core is crimped or bent into a helical shape, which can reduce the dimensional accuracy of the product and, as a result, prevent the magnetic properties from meeting the design specifications.

[0005] Patent Document 1 aims to provide a core material for a rotating machine that is excellent in bending workability and iron loss characteristics, and specifically describes that by adding 0.01 to 0.1% of Ti to ultra-low C steel, C is completely fixed, improving aging resistance and resulting in a material that is excellent in bending workability.

[0006] Patent Document 2 aims to provide, at low cost, a non-oriented electrical steel sheet that has excellent strength and magnetic properties and is suitable as an iron core material for electric vehicle motors. Specifically, it proposes punching a rotor and a stator from a non-oriented electrical steel sheet with a specific chemical composition, and then annealing only the stator to relieve strain, thereby achieving both high strength for the rotor and low iron loss for the stator.

[0007] Patent No. 4325235 Patent No. 5228379

[0008] Various studies have been conducted on non-oriented electrical steel sheets that have excellent magnetic properties, workability, or strength. However, Patent Document 1 requires the addition of Ti, which can have a detrimental effect on magnetic properties. Furthermore, Patent Document 2 punches out a rotor and a stator from the same steel sheet and performs stress relief annealing on only the stator. However, if the rotor and stator can be obtained from different steel sheets and combined, or if it is possible to appropriately select whether or not to perform stress relief annealing on the rotor and stator, the latitude in product design will be further expanded.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel non-oriented electrical steel sheet that has excellent magnetic aging resistance and is less likely to cause stretcher strain, a method for manufacturing the same, and a rotating electric machine including the same.

[0010] The present invention provides the following aspects: [1] The chemical composition, in mass%, is C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000% [2] A non-oriented electrical steel sheet according to [1], characterized in that the chemical composition further includes Mo: 0% to 0.0200%. [3] A non-oriented electrical steel sheet according to [1] or [2], characterized in that the chemical composition satisfies the following formula: Cev≦0.0055%.Cev = 12 × ([C (mass%)] / 12 + [N (mass%)] / 14 - [B (mass%)] / 11 - [Ti (mass%)] / 48 - [Cr (mass%)] / 104 - [Mo (mass%)] / 192) In the above formula, [element symbol (mass%)] indicates the content (mass%) of the element in the chemical composition. If the element is not included, substitute 0. [4] The chemical composition is, in mass %, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more types selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0. A method for producing the non-oriented electrical steel sheet according to any one of [1] to [3], characterized in that the non-oriented electrical steel sheet is produced by a process including steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and overaging treatment, the overaging temperature of the overaging treatment being 50°C to 500°C, and the temperature range of 50°C or higher being 10 seconds or longer. [5] A method for producing the non-oriented electrical steel sheet according to [4], characterized in that the chemical composition further includes Mo: 0% to 0.0200%. [6] The method for producing a non-oriented electrical steel sheet according to [4] or [5], characterized in that during the overaging treatment, bending is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm in at least a part of the step of holding the steel sheet in a temperature range of 50°C to 500°C. [7] The method for producing a non-oriented electrical steel sheet according to any one of [4] to [6], characterized in that after the overaging treatment, bending is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm.[8] The chemical composition is, in mass%, C: 0.0100% or less, Si: 2.6% or more and 4.5% or less, Mn: 0.10% or more and 3.00% or less, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% or more and 2.00% or less, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to A method for producing a non-oriented electrical steel sheet according to any one of [1] to [3], characterized in that the non-oriented electrical steel sheet is produced by a process including steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and bending, the bending being performed by pressing the steel sheet against rolls having a diameter of less than 500 mm. [9] A method for producing a non-oriented electrical steel sheet according to [8], characterized in that the chemical composition further includes Mo: 0% to 0.0200%.

[10] A rotating electrical machine having a stator, a rotor, and a housing that houses the stator and the rotor, wherein the stator core material or the rotor core material is the non-oriented electrical steel sheet according to any one of [1] to [3].

[0011] The non-oriented electrical steel sheet provided by the present invention has excellent magnetic aging resistance and is less likely to cause stretcher strain. Furthermore, the non-oriented electrical steel sheet can be obtained by the manufacturing method provided by the present invention. Furthermore, the rotating electric machine provided by the present invention has excellent magnetic aging resistance and is less likely to cause stretcher strain during processing. Here, "excellent magnetic aging resistance" typically refers to an iron loss degradation rate of less than 0.9. The iron loss degradation rate is the value obtained by dividing the increase in iron loss before and after aging treatment at 200°C for 24 hours by the iron loss before aging treatment. "Less likely to cause stretcher strain" corresponds to an A.I. of less than 40 MPa, as will be described in detail below.

[0012] FIG. 1 is a schematic diagram illustrating how to determine A.I.

[0013] The present invention will be described in detail for each of its constituent elements.

[0014] The reasons for limiting the chemical composition of the steel are as follows: In the following description, unless otherwise specified, the content of each element will be expressed in mass %, and the mass will be omitted.

[0015] <C: 0.0100% or Less> C increases iron loss and causes magnetic aging. Therefore, the C content is set to 0.0100% or less by mass, preferably 0.001 to 0.004% by mass.

[0016] <Si: 2.6% or more, 4.5% or less> Si increases the resistivity of steel and also reduces iron loss. To achieve this effect, a content of 2.6% or more is required. On the other hand, if the Si content exceeds 4.5%, the steel becomes embrittled and rollability deteriorates. Therefore, the Si content is set to 2.6 to 4.5%. Preferably, it is 3.0 to 3.5 mass%.

[0017] <Mn: 0.10% or more, 3.00% or less> Mn increases the resistivity of steel and also acts to coarsen sulfides and render them harmless. To achieve this effect, a content of 0.10% or more is necessary. On the other hand, if the Mn content exceeds 3.00% by mass, the magnetic flux density decreases, costs increase, and the steel is prone to cracking during cold rolling. Therefore, the Mn content is set to 0.10 to 3.00%. Preferably, it is 0.1 to 0.5% by mass.

[0018] <P: 0.15% or less> P is an element necessary for increasing the hardness of the steel sheet and improving punchability, but if added in excess of 0.15%, the steel sheet becomes embrittled, so the content is set to 0.15% or less, preferably 0.01 to 0.10%.

[0019] <S: 0.0040% or less> S is limited to 0.0040% or less. S precipitates in steel as sulfides, degrading grain growth and iron loss. If the S content exceeds 0.0040%, the degradation of grain growth and iron loss becomes significant, so the S content is limited to 0.004% or less. There is no particular lower limit, but it is difficult to achieve a content of 0.0005% or less using ordinary manufacturing methods. The S content is preferably 0.0010 to 0.0030%.

[0020] <N: 0.0040% or less> If N is contained in large amounts, it forms nitrides and deteriorates magnetic properties, so the upper limit must be set to 0.0040%. There is no particular lower limit, but considering current steelmaking technology, the lower limit is effectively 0.0001%. The preferred range is 0.0003 to 0.0020%.

[0021] <Al: 0.10% or more, 2.00% or less> Al is effective as a deoxidizer, and can also coarsen nitrides to render them harmless. Like Si, it also increases the resistivity of steel and reduces iron loss. To achieve these effects, 0.10% or more is required. However, if it exceeds 2.00%, the steel becomes embrittled and rollability deteriorates. Therefore, the Al content is set to 0.10 to 2.00%. Preferably, it is 0.20 to 1.50%.

[0022] <Sn and Sb: Total of one or both of 0% or more and 0.200% or less> Sn and Sb are effective in improving texture and suppressing nitriding and oxidation during annealing. Furthermore, at 0.005% or more, Sn and Sb suppress the movement of C, improving aging resistance. If the content is too high, the effect saturates and, further, there is an adverse effect on the embrittlement of the steel and the suppression of grain growth, so the total content is set to 0.200% or less. Preferably, it is 0.030 to 0.150%.

[0023] <Cr: 0.001% or more, 5.000% or less> Cr has the ability to form carbides and nitrides, and fixes solute C and N, thereby suppressing stretcher strain. Therefore, the lower limit is set to 0.001% or more. On the other hand, Cr reduces the saturation magnetic flux density of the steel sheet. If Cr exceeds 5.000%, the cost of adding Cr becomes a major issue, so the content is limited to 5.000% or less. A preferable range is 0.100 to 4.000%.

[0024] <Ni: 0% or more, 5.000% or less> Ni is an effective element that can increase the strength of steel sheets without significantly embrittlement. However, because it is expensive, it is added only in accordance with the strength required. When added, the upper limit is set to 5.000% in consideration of costs. Preferably, it is 1.000 to 4.000%.

[0025] <Cu: 0% or more, 5.000% or less> Cu increases the hardness of the steel sheet. If the content exceeds 5.000%, the cost of adding Cu becomes a significant issue, so the content is limited to 5.0% or less. The preferred range is 0.100 to 4.000%.

[0026] <Ca: 0% or more, 0.020% or less> Ca is intentionally added from the viewpoint of improving grain growth properties. However, since it is expensive, it is added only as needed. When added, the upper limit is set to 0.020% or less in consideration of costs. Preferably, it is 0.008% or less.

[0027] <Mg: 0% or more, 0.0200% or less> Mg is intentionally added from the viewpoint of improving grain growth properties. However, since Mg is expensive, it is added only as needed. When added, the upper limit is set to 0.0200% or less in consideration of costs. Preferably, it is 0.0080% or less.

[0028] <Rare Earth Elements (REM): 0% or More, 0.020% or Less> Rare earth elements are added for the purpose of improving grain growth by suppressing impurity precipitation. However, because they are expensive, they are added only as needed. When added, the upper limit is set to 0.020% in consideration of cost. Preferably, it is 0.001 to 0.008%.

[0029] <Ti: Less than 0.0100%> Ti has the ability to form carbides and nitrides, fixes solute C and solute N, and has the effect of suppressing stretcher strain. However, Ti forms fine nitrides or carbides, significantly impairs grain growth during stress relief annealing, and deteriorates magnetic properties, so the content is specified to be less than 0.0100%. Preferably, it is 0.0030% or less. Ti may be 0%, but may be unavoidably mixed in, so it may be 0.0020% or less.

[0030] <B: 0% or more, 0.0050% or less> When Al is added, it may precipitate as fine AlN, resulting in deterioration of magnetic properties, so B is added at the same time. If the B content exceeds 0.0050%, there is a risk of deterioration of magnetic properties due to excess B, so the upper limit is set to 0.0050%. Preferably, it is 0.0030 to 0.0040%.

[0031] <O: 0% or more, 0.0200% or less> O forms precipitates, hinders grain growth during annealing, and deteriorates magnetic properties, so the O content is set to 0.0200% or less. Preferably, it is set to 0.0030% or less. O may be 0%, but may be unavoidably mixed in, so it may be set to 0.0020% or less.

[0032] <Mo: 0% or more, 0.0200% or less> Mo has the ability to form carbides and nitrides, and fixes solute C and solute N, thereby suppressing stretcher strain. Therefore, Mo may be 0% or more, or may be 0.0030% or more. However, Mo forms precipitates that hinder grain growth during annealing and deteriorate magnetic properties, so the Mo content is specified to be 0.0200% or less.

[0033] The chemical composition of the non-oriented electrical steel sheet according to this embodiment may contain, in addition to the above elements, 0.10% or less each of Nb, V, Zr, Ce, Bi, and W, to the extent that the various properties of the non-oriented electrical steel sheet are not affected.

[0034] <Balance: Fe and Impurities> The balance is Fe and impurities. The impurities refer to elements that are mixed in from raw materials such as ore and scrap, or from the manufacturing environment, during industrial production of slabs or steel. This does not exclude the addition of known elements to replace Fe in the hope of achieving known effects, within a range that does not eliminate the effects of the present invention.

[0035] <Cev> Stretcher strain is caused by solute C and solute N. Cev, defined by the following formula, is an index related to solute C and solute N, and it is thought that stretcher strain is likely to occur if it is too large. Therefore, Cev is preferably ≦0.0055%. Cev may be 0.0054% or less, preferably 0.0025 or less, more preferably 0.0015 or less, and even more preferably 0.0000 or less. There is no limitation on the lower limit of Cev, but it may be −0.5861 or more. Cev = 12 × ([C (mass%)] / 12 + [N (mass%)] / 14 - [B (mass%)] / 11 - [Ti (mass%)] / 48 - [Cr (mass%)] / 104 - [Mo (mass%)] / 192) In the above formula, [element symbol (mass%)] indicates the content (mass%) of the element in question in the chemical composition of the non-oriented electrical steel sheet. For example, [C (mass%)] indicates the content (mass%) of C in the chemical composition of the non-oriented electrical steel sheet. Furthermore, if the element in question is not contained in the chemical composition of the non-oriented electrical steel sheet, 0 is substituted.

[0036] <A.I. Less than 40 MPa> The non-oriented electrical steel sheet according to this embodiment has an A.I. of less than 40 MPa. Here, A.I. is an abbreviation for Aging Index, and is sometimes referred to as the aging index. A.I. is determined by processing a JIS No. 13B tensile sample from a steel sheet, imparting 8% strain, and then aging at 100°C for 1 hour. The A.I. is calculated as the difference between the stress at 8% strain before aging and the lower yield point after aging. The strain is expressed as a percentage based on the original gauge length. The test speed is 7.2 mm / min. (equivalent to a strain rate of 0.002 / s with an original gauge length of 60 mm) under stroke control. FIG. 1 is a diagram illustrating a method for determining A.I. First, a tensile test is performed on the sample, imparting 8% strain at room temperature (23°C). The stress at 8% strain (i.e., the stress at 8% strain before aging) is recorded. The sample after the tensile test is then aged at 100°C for 1 hour, cooled to room temperature (23°C), and then subjected to another tensile test to break the sample. The lower yield point after aging is determined from the stress-strain curve in this tensile test, and the difference from the stress at 8% strain before aging is calculated. If a clear yield phenomenon and work hardening are observed in the stress-strain curve, the minimum stress between the yield phenomenon and the work hardening is taken as the lower yield point. If work hardening is not clear, as in Figure 1, the point with the lowest stress between the point at 2% lower elongation than the yield phenomenon and the elongation at break is taken as the lower yield point. Other measurement items are in accordance with JIS Z 2241 (2011). If the A.I. is 40 MPa or more, stretcher strain occurs during core processing, resulting in poor dimensional accuracy. Furthermore, magnetic aging occurs, and the magnetic properties deteriorate over time. Generally, the smaller the AI, the better the stretcher strain suppression effect and aging resistance. Therefore, AI is preferably 35 MPa or less, and more preferably 30 MPa or less.

[0037] <Manufacturing Conditions> Next, the reasons for limiting the manufacturing conditions in this invention and preferred manufacturing conditions will be described. Generally, the manufacturing method of a non-oriented electrical steel sheet includes the steps of steelmaking, slab casting, slab reheating, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, final annealing (finish annealing), overaging treatment and / or bending treatment, and application of an insulating coating. The steps may be performed in the order listed, or the order of the steps may be adjusted as appropriate.

[0038] (Steelmaking) The above-mentioned chemical composition is adjusted by a conventional steelmaking method such as converter steelmaking or degassing treatment.

[0039] (Slab Casting) Slab casting to obtain steel having the above chemical composition is performed by conventional continuous casting. Although it is not prohibited to apply blooming to continuously cast slabs to facilitate slab heating, this should be avoided as much as possible due to the increased cost.

[0040] In producing the slabs, the initial thickness is not particularly limited, but slabs having a thickness in the range of approximately 150 mm to 300 mm, preferably 200 mm to 250 mm, are produced by a known continuous casting method.

[0041] (Slab Reheating) The condition of the slab reheating temperature prior to hot rolling is very important for the production of non-oriented electrical steel sheets. This is because it is related to the solid solution and precipitation of impurity elements. In order to prevent the fine precipitation of compounds containing impurity elements, the slab reheating temperature is preferably 1250°C or less. Of course, if the absolute values ​​of the contents of major harmful elements such as S and N can be reduced, it is possible to increase the slab heating temperature, but this is not practical for industrial production.

[0042] (Hot rolling) The hot rolling conditions for slabs for non-oriented electrical steel sheets are, in principle, low-temperature extraction and high-temperature rolling, but by performing intermediate annealing, the coiling temperature does not need to be extremely high, and in fact, high-temperature rolling is not preferable from the viewpoint of descaling properties. That is, it is sufficient to apply conditions in which the finish entrance temperature in finish hot rolling is 900°C to 1000°C, the exit temperature is 830 to 900°C, and the coiling temperature is 600°C to 700°C.

[0043] (Annealing of hot-rolled sheet) It is possible to anneal a hot-rolled sheet. However, even if this annealing is applied, the magnetic properties in the rolling direction are improved, but not significantly, and the cost increases significantly. Therefore, whether or not to apply this annealing should be determined based on the desired properties.

[0044] (Pickling) Hot-rolled or hot-rolled annealed sheets can optionally be subjected to a descaling treatment before cold rolling or finish annealing to remove oxide, i.e., scale, layers that form on the steel sheet. Pickling is the most common descaling method, and involves chemically cleaning the steel sheet surface using an aqueous solution of one or more inorganic acids. While descaling is not prohibited, pickling may be unnecessary if the annealing atmosphere is favorable and the surface scale layer is rare.

[0045] (Cold Rolling) Cold rolling is performed once, or in two or more passes with annealing interposed therebetween. A single pass of cold rolling means performing one or more cold rolling passes without annealing in between. In either cold rolling, the final reduction is preferably set to 70 to 95%.

[0046] When cold rolling is carried out in two separate steps with annealing in between, the annealing is preferably carried out at 750 to 1200° C. for 30 seconds to 10 minutes.

[0047] When cold rolling with intermediate annealing is performed in two or more stages, the magnetic properties tend to become uniform. The number of cold rolling stages is appropriately selected taking into consideration the desired magnetic properties and production costs.

[0048] The thickness of the final product is obtained at this stage. Generally, the product thickness may be less than 0.35 mm. Taking into account the capacity and handling of each production facility, the minimum thickness may realistically be 0.20 mm. Note that once the final product thickness is determined, the thickness of the hot-rolled steel strip is automatically determined by the cold rolling reduction ratio.

[0049] (Final annealing: finish annealing) Finish annealing is greatly affected by time and temperature, and a higher temperature is better to shorten the annealing time, but currently, the maximum temperature is 1075°C as specified in the continuous annealing furnace equipment specifications. On the low temperature side, if the temperature is less than 950°C, a somewhat long soaking time is required. Furthermore, in order to improve the texture, a patent document (JP-B 06-051889) proposes heating to a temperature of 750 to 1150°C at a rate of 133°C / second or more. This technique is not precluded from being applied. If the holding time of finish annealing is less than 20 seconds, grain growth is insufficient, and if it exceeds 90 seconds, further grain growth does not occur, so the holding time is set to the range of 20 to 90 seconds.

[0050] (Overaging Treatment) By performing overaging treatment after finish annealing or during cooling of the finish annealing, solute C in the steel sheet bonds with Fe atoms to form cementite, which promotes the fixation of the solute C and improves the effect of suppressing magnetic aging and stretcher strain. The overaging temperature of the overaging treatment is 50°C or higher and 500°C or lower. If the temperature is lower than 50°C, the effect may not be sufficiently obtained, and if the temperature exceeds 500°C, the fixation of the solute C may not be maintained. The upper limit of the overaging temperature is preferably 300°C or lower. The lower limit may be 100°C or higher, and preferably 200°C or higher. The overaging treatment time is 10 seconds or longer. If the time is shorter than 10 seconds, the effect of the overaging treatment may not be sufficiently obtained. Although the upper limit of the overaging treatment time is not particularly limited, it is desirable to set it to 60 minutes or shorter because the effect saturates.

[0051] (Bending Treatment) By performing bending treatment after finish annealing, solute C and solute N in the steel sheet penetrate dislocations in the Fe atomic arrangement, promoting the fixation of the solute C and solute N, thereby improving the effect of suppressing magnetic aging and stretcher strain. Bending is performed by winding the steel sheet around a roll with a diameter of less than 500 mm. That is, bending is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm. Rolls with a diameter of 500 mm or more may not be able to bend the steel sheet sufficiently, and the effect may not be fully achieved. The lower limit of the roll diameter is not particularly limited, but since the smaller the diameter, the greater the bending becomes, and there is a risk of the steel sheet breaking, etc., it may be 300 mm or more. Furthermore, the bending angle of the steel sheet may be 5 degrees or more and 20 degrees or less, with the tangent direction at the point of contact between the roll cross-sectional circle and the steel sheet (the horizontal direction of the steel sheet surface in a flat state) as the reference (0 degrees). If it is less than 5 degrees, the steel sheet may not be bent sufficiently, and the effect may not be fully achieved. If the bending angle is too large, there is a risk of the steel sheet breaking, so it may be set to 20 degrees or less. The upper limit of the bending angle may be 15 degrees or less. The lower limit may be 8 degrees or more, or may be 10 degrees or more. Skin-pass bending differs from bending in the way that the Fe atomic arrangement in the steel is disturbed and the way in which dislocations are introduced, making it difficult to achieve the same effects as bending. Bending is also advantageous in terms of cost. The above effects can be achieved with just one bending process. Leveling is a process in which a steel sheet is wound around a roll. This process aims to straighten the coiled roll, eliminating any warping or bending of the coil and making it flat. Furthermore, the roll diameter is generally small, typically 100 mm or less. Therefore, leveling is different from the bending process of this embodiment.

[0052] The overaging treatment and the bending treatment may be used in combination. The overaging treatment and the bending may be performed simultaneously, or the bending may be performed after the overaging treatment. By using these treatments in combination, the effects of suppressing magnetic aging and stretcher strain can be synergistically improved.

[0053] (Insulating Coating Application) Since electrical steel sheets are used in a laminated state, an insulating coating may be applied to the surface to ensure interlayer resistance. Cr-containing insulating coatings have been used in the past, but Cr-free coatings have recently been developed, and either type may be used.

[0054] Molten steel was continuously cast to prepare a 250 mm thick slab for obtaining steel having the chemical composition shown in Table 1 below. The slab was then hot-rolled to produce a hot-rolled sheet. The slab reheating temperature was 1200°C, the finishing temperature in finish rolling was 850°C, and the coiling temperature was 650°C, resulting in a finished sheet thickness of 2.0 mm. The hot-rolled sheet was then annealed at 900°C for 1 minute as hot-rolled sheet annealing, descaled by pickling, and cold-rolled to a thickness of 0.25 mm. Finish annealing was then performed at 800°C for 30 seconds. The overaging treatment shown in Table 1 was then performed. Some samples were also bent by wrapping the steel sheet around a φ400 mm roll and passing it through the roll at a bending angle of 10 degrees (the tangent direction of the roll cross-sectional circle being 0 degrees). That is, the steel sheet was pressed against the roll to perform the bending process. The bending was performed during or after the overaging treatment when the overaging treatment was performed, and after the finish annealing when the overaging treatment was not performed. It was confirmed that the steel sheet (reference numeral 127) manufactured under the same conditions as the steel sheet reference numeral 101, except that the overaging treatment was performed during the cooling of the finish annealing, had magnetic properties and A.I. equivalent to those of the steel sheet reference numeral 101.

[0055] Next, the magnetic properties of iron loss W10 / 400 (iron loss at a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz) and magnetic flux density B50 (magnetic flux density at a magnetizing force of 5000 A / m) were measured. 55 mm square specimens were taken as measurement samples, and the average values ​​of the properties in the rolling direction and width direction were calculated. Magnetic measurements were performed using a device capable of measuring 55 mm square specimens conforming to the electromagnetic circuit described in JIS C 2556 (2015) and even smaller specimens. The measurement results are shown in Table 1. After magnetic measurement, the specimens were subjected to a magnetic measurement aging treatment at 200°C for 24 hours, and the iron loss W10 / 400 was measured. The increase in iron loss was divided by the iron loss W10 / 400 before aging treatment to determine the iron loss degradation rate after aging treatment, which is shown in Table 1. The AI ​​was also measured, and the results are shown in Table 1.

[0056] [Amendment under Rule 91 19.03.2025]

[0057] Reference numerals 101 to 122 and 127 have good components and AI. Reference numeral 123 has a high AI because it has not been subjected to either overaging or bending. Reference numerals 124 and 126 do not contain Cr and have a high AI. Reference numeral 125 has a high iron loss because its Ti content is outside the upper limit. Furthermore, the comparative examples with a high AI also tend to have a high iron loss degradation rate after aging.

[0058] To evaluate stretcher strain, the yield elongation (specified in JIS Z2241) in the pre-aging tensile test (8% strain) in the AI ​​test was examined. When yield elongation occurs, stretcher strain, which is a visible surface defect, occurs. In all cases where the AI ​​was less than 40 MPa, no yield elongation occurred, but in cases where the AI ​​was 40 MPa or more, yield elongation occurred. This shows that stretcher strain can be suppressed by lowering the AI ​​(less than 40 MPa). In the table, "---" in the "Yield Elongation" column indicates that yield elongation did not occur.

Claims

1. The chemical composition, in mass %, is as follows: C: 0.0100% or less, Si: 2.6% or more and 4.5% or less, Mn: 0.10% or more and 3.00% or less, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% or more and 2.00% or less, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0.020%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance consists of Fe and impurities. The difference in the lower yield point before and after aging treatment when subjected to aging treatment at 100°C for 1 hour after applying 8% strain: A.I. is less than 40 MPa. A non-oriented electrical steel sheet characterized by this.

2. The chemical composition of the non-oriented electrical steel sheet according to claim 1, further comprising Mo: 0% to 0.0200%.

3. The non-oriented electrical steel sheet according to claim 1 or 2, characterized in that Cev ≤ 0.0055% is satisfied by the following formula. Cev = 12×([C (mass%)] / 12 + [N (mass%)] / 14 - [B (mass%)] / 11 - [Ti (mass%)] / 48 - [Cr (mass%)] / 104 - [Mo (mass%)] / 192) In the above formula, [element symbol (mass%)] represents the content (mass%) of the element in the chemical composition, and 0 is substituted when the element is not contained.

4. The chemical composition is in mass %, C: 0.0100% or less, Si: 2.6% or more and 4.5% or less, Mn: 0.10% or more and 3.00% or less, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% or more and 2.00% or less, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0.020%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance: Fe and impurities. When manufacturing a non-oriented electrical steel sheet consisting of these, in a process including steelmaking, hot rolling, annealing of the hot-rolled sheet, pickling, cold rolling, finish annealing, and overaging treatment, the overaging temperature of the overaging treatment is set to 50°C to 500°C, and the temperature range of 50°C or more is set to 10 seconds or more. A method for manufacturing a non-oriented electrical steel sheet, which is the method for manufacturing a non-oriented electrical steel sheet according to any one of claims 1 to 3.

5. The method for manufacturing a non-oriented electrical steel sheet according to claim 4, wherein the chemical composition further contains Mo: 0% to 0.0200%.

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 4 or 5, wherein during the overaging treatment, in at least a part of the step of holding in the temperature range of 50°C to 500°C, bending is performed by pressing the steel sheet against a roll having a diameter of less than 500 mm.

7. The method for manufacturing a non-oriented electrical steel sheet according to any one of claims 4 to 6, wherein after the overaging treatment, bending is performed by pressing the steel sheet against a roll having a diameter of less than 500 mm.

8. The chemical composition is, by mass%, C: 0.0100% or less, Si: 2.6% or more and 4.5% or less, Mn: 0.10% or more and 3.00% or less, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% or more and 2.00% or less, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0.020%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance: an isotropic electromagnetic steel sheet composed of Fe and impurities is manufactured in a process including steelmaking, hot rolling, hot rolled sheet annealing, pickling, cold rolling, finish annealing, and bending. In the bending process, the bending is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm. A method for manufacturing an isotropic electromagnetic steel sheet, which manufactures the isotropic electromagnetic steel sheet according to any one of claims 1 to 3.

9. The method for manufacturing an isotropic electromagnetic steel sheet according to claim 8, wherein the chemical composition further contains Mo: 0% to 0.0200%.

10. A rotating electrical machine having a stator, a rotor, and a housing that houses the stator and the rotor, wherein the core material of the stator or the core material of the rotor is the isotropic electromagnetic steel sheet according to any one of claims 1 to 3.

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